Selective halogenation of 6-hydroxy picoline derivatives

Abstract

The invention relates to a method for selective halogenation of 6-hydroxy picoline derivatives such as 6-hydroxy picolinic acid and 6-hydroxy picoline. When 6-hydroxy picolinic acid is halogenated by allowing it to stand in an aqueous mineral acid solution for a sufficient period to replace the halo substituent with a hydroxy substituent, and then halogenated, an improved yield of the 3-halo, 6-hydroxy picolinic acid to the 5-halo 6-hydroxy picolinic acid is obtained.

What is claimed is: 
     
       1. A process for selective halogenation of a 6-hydroxy picoline derivative in the 3-position comprising: Allowing a 6-halo picoline derivative selected from the group consisting of 6-halo picolinic acid and 6-halo picoline to stand in an aqueous mineral acid solution for a sufficient period to replace the halo substituent with a hydroxy substituent, and halogenating the aqueous mineral acid solution of said 6-hydroxy picoline derivative to obtain the corresponding 3-halo 6-hydroxy picoline product.   
     
     
       2. The process of claim 1, wherein the halogenation proceeds at temperatures ranging from 25° to 200° C. 
     
     
       3. The process of claim 2, wherein the halogenation proceeds at temperatures ranging from 75° to 150° C. 
     
     
       4. The process of claim 1, wherein the halogenating gas is selected from chlorine and bromine. 
     
     
       5. The process of claim 1, wherein the mineral acid is sulfuric acid. 
     
     
       6. The process of claim 1, wherein said picoline derivative is 6-chloro picolinic acid, said halogenating material is chlorine, and the corresponding product is a mixture of 3-chloro-6-hydroxy picolinic acid and 5-chloro-6-hydroxy picolinic acid. 
     
     
       7. The process of claim 1, wherein said picoline derivative is 6-hydroxy picoline, said halogenating material is chlorine, and the corresponding product is 3-chloro-6-hydroxypicoline. 
     
     
       8. The process of claim 6, wherein the mixture of 3-chloro-6-hydroxy picolinic acid to 5-chloro-6-hydroxy picolinic acid is in a ratio of 5:1.